59 lines
2.3 KiB
Python
59 lines
2.3 KiB
Python
#!/usr/bin/env python3
|
|
"""shellmcp: an MCP server with one tool, `run`, that runs a bash command. Stdlib only, stdio.
|
|
|
|
--mode readonly (default) runs every command in a bubblewrap sandbox: the filesystem is
|
|
read-only except a private /tmp, there is no network, no other process is visible, and the
|
|
--hide paths (always ~/.ssh and ~/.gnupg) look empty. --mode all runs commands with the
|
|
user's full permissions; let the MCP client ask before each call.
|
|
"""
|
|
|
|
import argparse
|
|
import getpass
|
|
import json
|
|
import os
|
|
import shutil
|
|
import signal
|
|
import socket
|
|
import subprocess
|
|
import sys
|
|
|
|
ENV = {"PAGER": "cat", "GIT_PAGER": "cat", "NO_COLOR": "1", "TERM": "dumb"}
|
|
|
|
|
|
def cut(text, limit):
|
|
"""text, or its head and tail around a note when it is longer than limit."""
|
|
if len(text) <= limit:
|
|
return text
|
|
half = limit // 2
|
|
return f"{text[:half]}\n[... {len(text) - 2 * half} characters cut ...]\n{text[-half:]}"
|
|
|
|
|
|
def run(command, cwd, timeout=60, limit=8000, prefix=()):
|
|
"""The exit code and combined stdout and stderr of `bash -c command`, as one text."""
|
|
proc = subprocess.Popen([*prefix, "bash", "-c", command], cwd=cwd, stdin=subprocess.DEVNULL,
|
|
stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
|
|
env={**os.environ, **ENV}, start_new_session=True)
|
|
try:
|
|
out, _ = proc.communicate(timeout=timeout)
|
|
head = f"exit code {proc.returncode}"
|
|
except subprocess.TimeoutExpired:
|
|
os.killpg(proc.pid, signal.SIGKILL)
|
|
try:
|
|
out, _ = proc.communicate(timeout=5)
|
|
except subprocess.TimeoutExpired: # a process left the group and holds the pipe
|
|
out = b""
|
|
head = f"timed out after {timeout} s, killed"
|
|
return f"{head}\n{cut(out.decode(errors='replace'), limit)}"
|
|
|
|
def sandbox(cwd, hide=()):
|
|
"""The bwrap argv prefix of --mode readonly."""
|
|
argv = ["bwrap", "--ro-bind", "/", "/", "--dev", "/dev", "--proc", "/proc",
|
|
"--tmpfs", "/tmp", "--tmpfs", "/run", "--unshare-net", "--unshare-ipc",
|
|
"--unshare-pid", "--die-with-parent", "--new-session"]
|
|
for path in hide:
|
|
if os.path.isdir(path):
|
|
argv += ["--tmpfs", path]
|
|
elif os.path.exists(path):
|
|
argv += ["--ro-bind", "/dev/null", path]
|
|
return argv + ["--chdir", cwd]
|